1. Field of the Invention
The present invention relates to a signal transmitting device which converts an input signal into an output signal by detecting a change in intensity of a magnetic field caused by a change of the input signal as a change in magnetic resistance of a magneto-resistive element.
2. Description of the Related Art
A magnetic coupling-type isolator may be used as an isolator for transmitting a digital or analog signal, and is applied, e.g., to an interface for connecting a computer with its peripheral device, an interface for connecting between circuits of different potentials, or an interface for use in a relay transmission device on a communication network. The magnetic coupling-type isolator provides an electrical insulation between an input and an output, and also detects a change in intensity of the magnetic field caused by a change of the input signal as a change in magnetic resistance of a magneto-resistive element, so as to convert the input signal into an output signal. As an example of the magnetic coupling-type isolator, Japanese Patent Laid-open Publication (translation version) No 2003-526083 discloses a magnetic digital signal coupler which uses a magneto-resistive element having a memory effect. In the magnetic digital signal coupler disclosed therein, a pulse signal is generated at a time when a logic state of an input signal changes, and the pulse signal is input into the magneto-resistive element. According to this configuration, the magnetic resistance can be maintained over a period during which the logic state of the input signal remains unchanged.
The magnetic digital signal coupler described above, however, requires a circuit for generating a pulse signal at the time when the logic state of the input signal changes. This increases the circuit scale as well as cost. Furthermore, it has been pointed out that the coupler has poor reliability with respect to noise, because if false information is once stored in the magneto-resistive element due to the noise applied from the outside, the false information will be retained in the magneto-resistive element from the time of input of the noise to the time when the logic state of the input signal changes.